rip nobody responded

To elaborate, making good tutorials is hard (and also time-consuming), so really there doesn't exist a lot out there. In particular, optimizing for space is very much a "research" field, in the sense that new tricks are discovered all the time and any tutorial covering it is bound to be incomplete. For non-subframe electronics there exists the not-so-complete Complete Electronics Tutorial but it's, as mentioned, incomplete, and doesn't cover space optimization that well.

Modern, space-efficient TPT computers primarily exploit the fact that FILT can hold 29 bits of information at once, unlike SPRK that is only either on or off. As LBPHacker mentioned, the FILT wiki entry describes how this works. Going beyond this, however, takes a little work. Your best bet is to reverse-engineer other people's electronics, check the wiki for particles you aren't familiar with, and, when you're really confused, read the TPT source code (this process, incidentally, is how I learn about TPT computing). Also trial and error.

When reverse-engineering, you might want to keep the following in mind:

• Different processors have different bit widths. It's possible to make a significantly smaller computer simply by limiting yourself to 8 bits. (I'm looking at you, NoVIcE.)
• Many space efficient computers use a technique called stacking (a.k.a. layering). I talked about it a little in my tutorial series (~2245936), but you don't need it to make (relatively) small computers (NoVIcE's 8-bit computer (~2169745) and my old 29-bit computer (~1570768) don't use it, for example). You can tell if stacking is used by ctrl-right-click-dragging over the whole computer and seeing if there are any particles left (if there are particles left, then stacking has been used).
• TPT mechanics are really finicky. You might have a working component, but after you exit the game and reload it the next day, the whole thing stops working because of some timing issue. You will want to frequently reload particle order, which means, basically, to local save (not stamp) and local load (not reload). I talked aboout it in the context of subframe in my tutorial series as well (~2235222).
• By now, you might be wondering what subframe is. Most computers don't use subframe, but a few modern ones do. Those work very differently from classical computers, and would confuse you horribly if you don't have basic knowledge about how subframe works. Usually you can tell that a computer uses subframe by looking for the "subframe" tag. It's up to you whether you want to pursue the subframe route, but subframe allows your electronics to be orders of magnitude faster (and, with advanced techniques, possibly more compact), and is a lot more intuitive to work with once you know how it works (though learning it is difficult).

Here are some existing computers that you might want to try to reverse-engineer. Note that you can find all of these by searching "processor" or "computer" in TPT.

Synergy's computer (29-bit, no subframe, no stacking)

NoVIcE's computer (8-bit, no subframe, yes stacking)

poodiepie's computer (16-bit, no subframe, no stacking)

drakide's computer (5-bit, no subframe, no stacking, no FILT data, but I put it here because it uses a totally different design idea to keep small)

LBPHacker's computer (29-bit, yes subframe, yes stacking)

If you want to chat about TPT electronics, feel free to PM me, or join us on IRC (there's a wiki page for that). Though, I am strongly biased towards subframe electronics, so I might not be able to talk a lot about classical eletronics. Also, as mentioned, there aren't many tutorials around, but you can help to solve that! When you have gotten a better hold of TPT electronics, you should try to write your own tutorials too.